Cellulose is one of the most abundant, renewable organic raw materials in the world. However, the use of cellulose still has not reached its potential in many areas of application. One major reason that it has not been more widely used is that for most applications natural or unmodified cellulose is unsuitable and cellulose derivatives must be used. In order to prepare cellulose derivatives it is often necessary to first dissolve the cellulose and then to transform it into the desired products in solution. Although various methods and techniques for dissolving cellulose do exist, the methods or techniques are often cumbersome and expensive. As a result, the use of cellulose derivatives is often more expensive than the use of alternative materials which compete for the same applications.
The efficiency of existing methods of preparing cellulose derivatives, such as cellulose ethers, on an industrial scale could be greatly improved by the availability of a suitable organic solvent for the unmodified cellulose. Presently, modified cellulose in the form of a sodium cellulose is required as a starting material in all cellulose ether preparations. This must be subjected to a nucleophilic substitution reaction with an alkyl halide or the ring opening addition of an alkylene oxide. Reactions of this type presently are being conducted under heterogeneous conditions in aqueous or organic media. This results in unfavorable reaction kinetics, a loss in reaction efficiency (less than 40%), domination of by-product formation (50% of reacting reagents are lost to the formation of by-products), and very poor yields. In addition, because of the sodium chloride by-product, expensive reactor autoclaves are required.
Cellulose, because of strong hydrogen bonding and high crystallinity, is insoluble in most solvents. In fact, cellulose is soluble only in a few aqueous solvents, such as copper ammonium hydroxide, quaternary ammonium hydroxide, and several transition metal complexes. Many of the problems encountered in the preparation of cellulose derivatives could be greatly reduced or eliminated by the use of an organic solvent for cellulose which permits the formation of homogeneous organic solutions of unmodified cellulose.